Reduce boilerplate when creating simple mojom::URLLoaders.

mojo/public/cpp/system/data_pipe.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file provides a C++ wrapping around the Mojo C API for data pipes,
 // replacing the prefix of "Mojo" with a "mojo" namespace, and using more
 // strongly-typed representations of |MojoHandle|s.
 //
 // Please see "mojo/public/c/system/data_pipe.h" for complete documentation of
 // the API.
@@ skipping 116 matching lines @@
   return MojoEndReadData(data_pipe_consumer.value(), num_bytes_read);
 }
 
 // A wrapper class that automatically creates a data pipe and owns both handles.
 // TODO(vtl): Make an even more friendly version? (Maybe templatized for a
 // particular type instead of some "element"? Maybe functions that take
 // vectors?)
 class DataPipe {
  public:
   DataPipe();
+  explicit DataPipe(uint32_t capacity_num_bytes);
   explicit DataPipe(const MojoCreateDataPipeOptions& options);
   ~DataPipe();
 
   ScopedDataPipeProducerHandle producer_handle;
   ScopedDataPipeConsumerHandle consumer_handle;
 };
 
 inline DataPipe::DataPipe() {
   MojoResult result =
       CreateDataPipe(nullptr, &producer_handle, &consumer_handle);
   ALLOW_UNUSED_LOCAL(result);
   DCHECK_EQ(MOJO_RESULT_OK, result);
 }
 
+inline DataPipe::DataPipe(uint32_t capacity_num_bytes) {
+  MojoCreateDataPipeOptions options;
+  options.struct_size = sizeof(MojoCreateDataPipeOptions);
+  options.flags = MOJO_CREATE_DATA_PIPE_OPTIONS_FLAG_NONE;
+  options.element_num_bytes = 1;
+  options.capacity_num_bytes = capacity_num_bytes;
+  mojo::DataPipe data_pipe(options);
+  MojoResult result =
+      CreateDataPipe(&options, &producer_handle, &consumer_handle);
+  ALLOW_UNUSED_LOCAL(result);
+  DCHECK_EQ(MOJO_RESULT_OK, result);
+}
+
 inline DataPipe::DataPipe(const MojoCreateDataPipeOptions& options) {
   MojoResult result =
       CreateDataPipe(&options, &producer_handle, &consumer_handle);
   ALLOW_UNUSED_LOCAL(result);
   DCHECK_EQ(MOJO_RESULT_OK, result);
 }
 
 inline DataPipe::~DataPipe() {
 }
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_SYSTEM_DATA_PIPE_H_